Maps and Cartographic Representation

1.1 What is a Map

A map is defined as a representation of the whole or a part of an area. Maps are usually prepared on a flat surface, but globes are also maps in that they represent the entire earth. Although we think of maps as depicting geographical areas, they can also be used to represent other areas, such as the heavens or parts of the human body. We therefore say that explorers map the earth, astronomers map the heavens, and geneticists map chromosomes. For our purposes in Cartographic Connections, we consider a map any representation of a geographic area – that is, a part or all of the earth’s surface. That surface usually contains many things that the map maker wants us to see in one image, for example, roads, cities, and lakes. Maps above all help us to graphically display spatial relationships. By using a map, we can show the relationship between one feature -- such as a mountain -- to others, such as rivers or cities. Maps can depict many types of phenomena in the encounter between people and place. They may reveal natural encounters as people represent the physical environment, cultural encounters as they show where two or more groups of people interact, political encounters as two or more nations come in contact, and technological encounters as a result of humankind’s ingenuity in developing transportation systems, agricultural areas, and mining locations.

Maps are most often drawn or printed on paper, but they may also be produced on any surface. They may be drawn in the sand or on leather hides. In some parts of the world, people make maps out of anything handy, for example, sticks or other objects. As long as they show a place, and can help people understand the relationship between spatial phenomena, they are really maps. Some maps take even more unusual forms. Certain archaeologists believe that some petroglyphs (images incised into rock surfaces) and pictographs (images painted on rock surfaces) may be maps because they appear to show information about places, such as hunting areas, water holes, and routes of travel. Because all people think in terms of where things are in relationship to where other things are (for example home in relation to school) we should realize that many maps are never produced in flat form at all but are only in our minds; these are called “mental maps.”

We commonly use them to communicate graphic information about places to others. Maps are used for many purposes in daily life -- to help people navigate from place to place, to identify real estate, to indicate areas where certain things (like coal or oil) are found. Politicians use maps to show territories of their political constituents, and advertisers may use maps to direct us to their products and services.

Cartographers make maps. You become a cartographer when you draw a map to help someone find your home. This happens when you translate your mental map into a graphic representation by taking pencil to paper and showing where things are in relationship to each other. Because you draw that map by hand and make only one copy, it is considered a “manuscript map.” If you were to produce a number of copies (on a printing press or your computer) it would be a “printed” map.

When you draw a map, you become part of a long tradition stretching back thousands of years. You join other cartographers in the field called cartography – the art and science of map making. Although we may be prone to associate maps with particular periods in world history, such as the age of European exploration, it is safe to say that all peoples make and use maps of some type.

1.2 Maps are Unique

It is difficult to get an overview of an area in any way other than consulting by map. A map places spatial data i.e. data about objects or phenomena for the location on the earth is known in their correct relationship to one another. A map can be considered as a spatial information system that gives answers to many questions concerning the area depicted: the distance between points, the position of points in respect with each other, the size of areas and the nature of distribution patterns.

1.2.1 Values of Maps

Maps are perhaps as fundamental to society as language and the written word. They are the preeminent means of recording and communicating information about the location and spatial characteristics of the natural world and of society and culture. Some would say that the use of maps distinguishes geoscience from all other disciplines. The truth is that maps, though of special concern to surveyors and geographers, are used throughout the sciences and humanities and in virtually every aspect of day-to-day life. Millions of maps are produced and used annually throughout the world by scientists, scholars, governments, and businesses to meet environmental, economic, political, and social needs. Many cartographers have reflected on the important role played by maps in society.

Maps gain their value in the three ways:

a) As a way of recording and storing information

Governments, businesses, and society as large must store large quantities of information about the environment and the location of natural resources, capital assets, and people. Included are plot, parcel, and cadastral maps to record property, maps of society's infrastructure or utilities for water, power, and telephone, and transportation, and census maps of population.

b) As a means of analyzing locational distributions and spatial patterns

Maps let us recognize spatial distributions and relationships and make it possible for us to visualize and hence conceptualize patterns and processes that operate through space.

c) As a method of presenting information and communicating findings

Maps allow us to convey information and findings that are difficult to express verbally. Maps can also be used to convince and persuade, or even propagandize.

To realize this potential, it is useful to learn some basic principles of cartographic communication and map design. Cartography is a special type of communication that does require training. But, attention invested in learning the basics will pay off handsomely in the production of more effective maps. Sometimes people assume that such training is too highly technical to be mastered easily and forego the use of maps. This is unfortunate because maps could be used more widely in the natural sciences, social sciences, and humanities for analysis and communication, particularly now that computers can be used as an aid to production. Some attention to first principles is still warranted.

1.2.2 Maps as information products

Maps provide us with information, meaning they help us find, confirm, and explain answers to questions like the ones in the preceding section. Consequently, they are information products. In economy, three fundamental questions are used to characterize products in general

1. What is produced?

2. How is it produced?

3. For whom is it produced?

They can be adapted to cartography with this question that guides the cartographic production process: How do I say what to whom? The following table analyses this question and in doing so opposes traditional and modern techniques. This reveals some fundamental changes in the visualization process.

1.2.3 Map Functions

Traditionally, maps are used as aids to navigation, as reference documents, and as wall decorations. Maps have four functions/roles today:

a) Data display: maps provide useful ways of displaying information in a meaningful way in practice, the cost of making and printing a map is high, so its contents are often a compromise between different needs

b) Data stores: as a means of storing data, maps can be very efficient, high density stores, a typical 1:50,000 map might have 1,000 place names on it. The distances between all possible pairs of these 1,000 places would run to (1,000 x 999 / 2) or 499,500 numbers if stored in a table instead of scaled off the map when needed. The information printed on the typical 1:50,000 topographic map sheet requires 25 million bytes (25 MB) of storage when it is converted to digital form, equivalent to one standard computer tape

c) Spatial indexes: a map can show the boundaries of areas (e.g. land use zones, soil or rock types) and identify each area with a label. a separate manual with corresponding entries may provide greater detail about each area

d) Data analysis tool: maps are used in analysis to make or test hypotheses, such as the identification of cancer clusters and examine the relationship between two distributions using simple transparent overlays

1.2.4 Map Uses

· The most important use of the maps is in orientation and navigation i.e. people use maps for getting from one place to one another along a plotted route, and want to be able to check with the help of the map whether they are still on course during their trip.

· Maps are used for physical planning: - i.e. maps inventorize the present situation; define development process, propositions of the future situations (future land use).

· Maps are used for management tasks or monitoring: - they are large scale maps e.. road maintenance maps, canals and airport.

· For education objectives, special purpose map are produced- school atlases, wall maps workbooks.

· Codification: show legal situation as regards property rights e.g. cadastral maps with function of codifying land ownership.

· Maps with interfaces like databases. Maps have been used as graphical interfaces to the data banks in which the spatial information was stored.

Conditions for proper use of the maps

When one to profit from this power of maps, certain conditions have to be met:

a) One should be familiar with suitable map use strategies e.g. relationship between mapped objects, their conditions and themselves.

b) One should have access to the relevant data sets.

c) Meta-information on data quality should be available to assist in the decision making process.

d) It is possible to integrate the various data sets, if necessary by modeling them (for instance, generalization).

1.3 Map Classification

• Maps based on main functions (orientation, physical planning, forecasts, management and education

• Maps grouped according to similarity in the specific methods used (chroropleth method or the isoline method)

• Maps according to the themes:- physical planning maps, town plans, weather charts, geological maps, population maps, language maps etc.

The elements of definition of a map are spatial information, graphic representation, scale and symbols.

Ø A map is a graphic model of the spatial aspects of reality.

Ø A map is a convectional image, mostly on a plane, of concrete or abstract phenomena, which can be located on space. By conventional one works with convention like sea is represented by blue, north is at the top.

Ø Scale, confusion exists about the concepts large scale and small scale - In every day linguistic usage, small scale is linked with small areas but in mapping this is used in the reverse sense. Small scale are linked with large areas that are represented on the map area. A large scale can be connected with a small area with a detailed data on a relatively large map area

1.3.1 Topographic and Thematic maps

Topographic maps supply a general image of the earth’s surface; roads, rivers, building, vegetation, relief, names etc. Thematic maps represent the distribution of one particular phenomenon. Very thematic map, as a basis needs topography information often this is provided by a topographic map where minor features have been omitted. A thematic map would also emerge if one aspect of the topographic maps (such as motor ways) is highlighted, so that the other categories of data on map are perceived as ground.

In digital environment the differentiation between topographic maps and thematic maps is less relevant, as both map types consist of number of layers: a topographic map would be a combination of separate road and railway layers, a settlement layers, hydrography, contour, names layer etc. each of these layers would be thematic map in its self and a combination of layers in which each data category had the same visual weight, would be a topographic map. If one category were to be graphically emphasized on a highlighted and the others there by relegated to the status of ground, then it would again change into thematic map

1.3.2 Permanent, Virtual, Temporal and Mental maps

People form for themselves a mental model of reality e.g. whilst living in the village one would form while traversing the village on a daily basis a mental construct, which operates like a virtual map when a visitor asks for direction, one would consult this mental construct in order to provide an answer. Answering the question could also be done by drawing sketch maps, which is a permanent print-out from our mental construct of reality, designed for answering specific request.

Such a mental construct cannot only be generated from ones contact with reality but also through consulting a proper, tangible paper map (a permanent map, or hand copy map). When one is an experienced map user, one would be able to grasp the essential information from a paper map and store this in one’ mind.

This process can also take place from the map displayed temporarily on a monitor screen (a temporal map, which is visible but not tangible) this temporal maps may be generated from spatial database stored in the computer, from which a specific selection has been made in order to answer specific requirements or objectives. This spatial database that can be used to produce other maps, function as a virtual map.

Maps can be said to show three dimensions of the phenomena represented: the nature or the value of the objects (that’s the attributes) and their location (x, y coordinates) it is one of the tasks of cartography to have the representation of the attributes stand out sufficiently on the flat paper or monitor screen surface.

1.4 Map Types

It is important to know the different map types as it gives an insight on the display types, source of data, and how to collect data. Maps can be classified according to their purposes, method of production, and the scale of map. In practice we normally think of two types of map: topographic and thematic maps, which can be presented as line or photo maps and can be stored in hardcopy or softcopy

1.4.1 Topographical maps

These are general maps that portray a section of the earth’s surface and accompanying features. These features usually represent the visible landscape and terrain. Are large-scale general maps of land areas. Generally maps have the objectives to portray the spatial relationship of different geographical features e.g. roads, water bodies, boundaries, etc. They are made in series of individual sheets with high accuracy by photogram metric means

They act a reference tool, showing the outlines of selected natural and man-made features of the Earth. often acts as a frame for other information. "Topography" refers to the shape of the surface, represented by contours and/or shading, but topographic maps also show roads and other prominent features

Since they have positional accuracy, they are required for site location, engineering purposes, and they have the validity of legal documents and basis for boundary determination, transfer of ownership, tax assessment etc tourism, representation of relief etc

1.4.2 Thematic maps

These are more specific than topographical maps. Thematic maps depict information that may or may not be directly observable such i.e. a tool to communicate geographical concepts such as the distribution of population densities, climate, movement of goods, land use, forest type, amount of rainfall, etc

As general maps attempts to portray the positional relationship of a variety of different attributes on the map , Thematic maps concentrates on spatial variations of a single attribute or the relationship among several. There is no limit to subject matter and they are commonly small-scale maps. They help in understanding a specific attribute e.g. roads of Uganda

1.4.3 Line Maps

These are maps that are produced using points, lines and polygons. They can be any of the above but the end product should be in vector format i.e. features composed of lines, points and areas

Advantage: they are neat and Disadvantage: they leave attribute which are not line e.g. relief

1.4.4 Photo maps / space amps / image maps

These are maps that have an image as the background. It is combined of a controlled photo mosaic and map detail (enhancements). The base map be aerial photography or satellite images. a photo map is derived from a photographic image taken from the air. Features are interpreted by the eye as it views the map. Certain features may be identified by overprinting labels

Advantage: they are quicker to produce and may show detail of other areas that a line map cannot show

Disadvantage: high buildings in urban areas, shadow, relief inversion and scale limits for detail. They are rarely completely free of distortions

N.B. Photo/satellite image is a direct representation, contains more information, needs a specialist and has direct information on ground.

1.4.5 Orthophoto maps

These maps show land features using color-enhanced photographic images which have been processed to show detail in true position. They may or may not include contours. Because imagery naturally depicts an area in a more true-to-life manner than the conventional line map, the orthophoto map provides an excellent portrayal of extensive areas of sand, marsh, or flat agricultural areas.

1.4.6 Physical maps

Physical maps show the earth's landforms and bodies of water. The maps use lines, shading, tints, spot elevations, and different colors to show elevation and distinguish the mountains from the lowlands.

This kind of map often has some road, city and cultural information but mostly functions as a view of the land surface. Often these maps make very attractive framed pieces for the den or office.

1.4.7 Political maps

Political maps show boundaries that divide one political entity from another, such as townships, counties, cities, and states. Some maps emphasize the boundaries by printing the areas of each political division in different colors, for example world maps usually show each country in a different color.

A political map can be made of any area from the local county, municipal levels all the way up to the world level. In general, most maps are political with far fewer being produced as physical maps.

1.4.8 Relief maps

Relief maps are maps that show relief data using contour lines, colors, and/or shading to evidence the elevation.

Shaded relief maps show topographic features by using shading to simulate the appearance of sunlight and shadows. Steep mountains will have dark shadows, while flat lands will have no shadows.

Raised-relief maps are three-dimensional plastic or vinyl maps portraying the physical features of a region. Raised relief maps can have as much as 2-3 inches of vertical relief, while this type of map is neat to look at they are all but impossible to ship so we cannot offer them on this site. In fact we rarely carry them in our store as we had upwards of 50% of them arrive in the "flattened relief" condition.

1.4.9 Road maps

Michelin in France and Gulf Oil in America produced the first road maps to encourage people to travel more, thus consuming more tires and oil. Such maps were usually free until the oil crisis of 1973, when service stations began to charge for their maps.

A road map is published primarily to assist travelers in moving from one place to another. Some road maps show only interstate highways, while others show a detailed network of roads, including the back roads. Generally, only large-scale maps - such as a topographic map, a Gem Trek map, Trails Illustrated map, or a DeLorme Atlas and Gazetteer - will show unimproved roads.

Some road maps specify distances between various points on the map. Others show various cultural geography features such as colleges and universities, airports, museums, historical sights, and information to make a journey more interesting.

You will discover several publishers that have produced entire series of road maps for given regions. Examples include the Michelin series for France or the Mairs series for Germany.

Road atlases are frequently a good choice for a traveler who is going to be covering a large region. There are two main types of road atlases: state or national atlases, and city street atlases.

1.4.10 Softcopy and Hardcopy Map

Softcopy (digital map) can be topographic or thematic in digital format or computer compatible format. Digital map is limited with screen size: but zoom and pan are available if required to increased resolution. Number of screen colors (usually a minimum of 256). They are easy to change scale and correct errors.

Under hardcopy is output can be printed on plain paper, Plane bond, Glossy paper, Clear Mylar, etc using Laser printers, Ink-jet (and wax) printer, design jets, pen plotters, etc and quality is determined in dot per inch (dpi); 300, 600 and 1200 are commonly available, and useful for photographic type output and sharper text.

1.5 Thematic Maps

There are many types of thematic maps but let us look at main ones

1.5.1 Area class map

An area class map shows zones of constant attributes, such as vegetation, soil type, or forest species. The boundaries are different for each map as they are determined by the variation of the attribute being mapped, e.g. breaks of soil type may occur independently of breaks of vegetation

1.5.2 Choropleth map

Choropleth map is a map which shows differences by using shading or colors. It is a thematic map in which areas are shaded or patterned in proportion to the measurement of the statistical variable being displayed on the map, such as population density or per-capita income. It provides an easy way to visualize how a measurement varies across a geographic area

It uses reporting zones such as counties or census tracts to show data such as average incomes, percent female, or rates of mortality. The boundaries of the zones are established independently of the data, and may be used to report many different sets of data.

Let us look at example of choropleth map shows population data for some of the departments of metropolitan France

Choropleth maps are the prototypical thematic maps. The name is composed of the Greek words plethus meaning quantity and choros meaning space. Choropleth maps depict attributes related to regions. They show the values of these attributes, i.e. the quantities, by areal symbols. These are shadings, colors, or patterns. Here is an example of a choropleth map.

A problem is that some count values depend on region size. If the size of enumeration units is not as homogeneous as the size of counties in the map of Georgia, comparisons become difficult or uninteresting.

You would probably not be surprised to hear that the population in the USA is bigger than in Monaco, because Monaco is much smaller than the USA.

A more interesting comparison between the two countries is one that eliminates the effect of different region size, as is done with population density. Density figures report the population referring to an area of equal size, say one square kilometer. You divide the population figure of each region by the size of that region, resulting, for example, in population per square kilometer. The principle of adjusting raw totals for differing sizes of enumeration units is called standardization.

But pay attention only to use standardization when the count value actually depends on the region size. This is, for example, not true for the number of days with sunshine: a bigger country would not have more days with sunshine than a smaller one due to the difference in size.

The following two maps show the effect of standardization. In the left map, total numbers are depicted without standardization. The big dark colored district in the southeast has a high value; it belongs to the highest class. In the right map, where the population figures have been standardized by the area this district appears in the light color of the lowest class. This reveals that the large number of inhabitants was caused by the size of the region. Such drastic changes are less likely for smaller regions: compare the two maps.

Pros and cons of choropleth maps

• + easy to produce and read

• + distribution patterns are easy to recognize

• - badly misleading if inappropriately standardized

• - cannot show variability within regions

• - regions are often not appropriate for a theme

• - most common pitfall: colors for quantities

1.5.3 Proportional Symbol Maps

Proportional symbol maps present data by symbols or diagrams located at points. The size of the symbol reflects the amount of the phenomenon. Here is an example of a proportional symbol map, using the most popular symbol, the circle. It shows the same information as the choropleth map of Georgia's total population in the previous section.

The data are not standardized. This could be done, for example, by dividing them by the area. In this example, the point data are conceptual, because they do not refer to a point, but describe an areal phenomenon. The symbols are geometric.

The scaling is mathematical and thus does not account for the psychological effect of underestimating large symbols. But perceptual scaling would have enlarged the already large circles in the northern area, where cluttering occurs. In other parts of the map, the circles are nearly invisible - a problem of the wide range covered by the raw data. In order to avoid this effect, the data could be classed so that a fixed number of symbols results, which can be drawn in reasonable sizes.

Pros and cons of proportional symbol maps

• + large, open-ended choice of possible symbols from circles through bars to Chernoff faces etc.

• + no need to aggregate data to fixed regional units

• - distribution patterns can be difficult to recognize

• - danger of visual clutter

1.5.4 Isopleth map

An isopleth map shows an imaginary surface by means of lines joining points of equal value, "isolines" (e.g. contours on a topographic map). used for phenomena which vary smoothly across the map, such as temperature, pressure, rainfall or population density

Isopleth maps are used to depict smooth continuous phenomena. These phenomena are represented by interpolating lines of equal values (isolines). The name "isopleth" is specifically used when conceptual point data are represented, i.e. values are not measured at point locations, but collected over areas. Otherwise, the term "isometric" is used. Smooth continuous phenomena are, for example, height and temperature. They are measured at point locations, i.e. they are true point data. The interpolation leads to lines of equal height (contour lines) or lines of equal temperature (isothermes). Probably you have already seen such isolines on topographic maps and weather maps. If conceptual point data shall be interpolated, they must be standardized in order to account for the area over which they have been collected. Isopleth maps can be misused when applied to non-continuous phenomena. Consider population data that are collected on basis of enumeration units, for example in the area of São Paulo. For each unit a figure representing the population density in this unit is available.

The next graphic shows an isopleth map. A centroid has been placed in each unit and the population density figure has been attached to it. Then isopleths have been interpolated between the centroids. This gives the impression that, for example, in the city of São Paulo population density gradually changes northwards and southwards.

But this differentiation within the enumeration units is not contained in the data; it is only an artefact. A choropleth map is an appropriate depiction of the data, because the data only provides one value for each unit.

There are various methods of interpolation:

• manual

• triangulation

• inverse-distance weighting

• kriging (optimal interpolation)

And there are different ways to symbolize the interpolated data.

• contour lines

• triangulation

• hypsometric tint

• continuous-tone map

• fishnet

Pros and cons of the interpolation method

• + familiar from topographic maps (terrain representation)

• + one type of map for continuous phenomena

• - often misused

• - suggesting detail that is not there

1.5.5 Dot Maps

Dot maps have become increasingly popular. They are a good alternative for choropleth maps. Each dot in a dot map represents a fixed value. For population data, for example, this can be one inhabitant or any other amount. If additional information on location is available, it can be used for positioning the dots. Thus it can, for example, be avoided to place inhabitants in lakes. For the following example no additional information was available.

Pros and cons of dot maps

• + show finer detail, actual distribution patterns

• + production made easier through GIS

• - information needs

• - unfamiliar

1.6 Topographic Cartography

One of the most widely used map types is the topographic map. Indeed, the wide range of information provided by topographic maps makes them extremely useful to both professional and recreational map users.

Topographic maps are used as basic tools for planning and executing projects. They are of prime importance in planning settlements, airports, highways, dams, pipelines, transmission lines, industrial plants, and countless other types of construction. They are an essential part of ecological studies and environmental control, geologic research, studies of the quantity and quality of water, and projects for flood control, soil conservation, and reforestation. Intelligent and efficient development of our natural resources depends on the availability of adequate topographic maps. Topographic maps are also utilized by outdoor enthusiasts, including hunters and hikers, to show relief features, wooded areas, and watercourses.

A topographic map is a graphic representation of the three dimensional configuration of the earth’s surface. It shows size, shape and distribution of landscape features, and presents the horizontal and vertical positions of those represented features.

Features on topographic maps can be divided into three major groups:

• Relief: Depicted with brown contour lines that show hills, valleys, mountains, plains, etc. Elevations are given in meters (or feet) above mean sea level. There are also spot elevations (shown in black), where lake level, summit of a hill or road intersections are marked for elevation.

• Water features: Depicted in blue, they represent oceans, lakes, rivers, streams, swamps, etc.

• Cultural features: Depicted in black, they represent all the man-made features: buildings, roads, railroads, land boundaries, etc.

Note that topographic maps are distinguished from planimetric maps by the addition of relief in measurable form.

Find below some extracts of topographic maps from different countries. Observe the difference in color, typography, detail, etc.

1.6.1 Intentions of Topographic Map

A topographic map provides information on the existence, the location, and the distance between features. It also indicates variations in terrain, heights of natural features, and the extent of vegetation cover. Therefore, topographic maps have many intentions, but the first is still to give a graphic representation of a portion of the earth's surface drawn to scale. This ideal representation would be realized if every mapped feature of the area could be shown in true shape. Obviously, this is impossible: if each feature was represented in true shape, the map would result in a product impossible to read, even with a magnifying glass. This is why the map has to be generalized.

Note: Topographic maps are often used as background information in thematic cartography.

1.6.2 Topographic Map versus Reality

Shown on the following example, how a topographic map provides a graphic representation of a portion of earth's surface. You will see that the main characteristics of the reality are preserved in the topographic map, and that all features are at the same level of importance (contrary to a thematic map). However, most of the features go through the generalization process and are therefore distorted. Take a look at transverse valley of Moutier both as picture and map

1.6.3 Classes of Topographic Maps

According to International Cartographic Association (1984) it is possible to classify topographic maps as being either:

• Official Cartography: maps that are edited by official institutions such as Department of Lands and Surveys, Entebbe (Uganda), Bundesamt für Landestopographie (Switzerland), etc.

• Commercial Cartography: maps that are edited by private companies as Informatics Developers (Uganda), Orell Füssli (Switzerland), etc..

Another important classification criterion is the scale. One can differentiate within topographic maps:

• Large scale: larger than 1:25 000

• Medium scale: 1:25 000 to approximately 1:250 000

• Small scale: smaller than 1:250 000 to approximately 1:2 500 000

• Very small scale: smaller than 1:2 500 000, usually atlas-maps

1.7 Components / Features of Maps

Maps often consist of a combination of words and images that work together to help us to locate, and to better understand, places

1.7.1 Mapped area

The first part of the map that may catch your attention is the geographic subject of the map itself, map detail, or mapped area

1.7.2 Inset

Some maps actually feature not only this mapped area, but may also contain an inset (or insets) showing an enlargement of some important area, such as a harbor, battlefield, or city.

1.7.3 Contour lines

Topography is the elevation of the land surface, and it is shown on topographic maps with contour lines, which are drawn in brown. A contour line is an imaginary line on the surface of the Earth connecting points of equal elevation.

1.7.4 Color

The colors on a topographic map are symbolic of different map features.

• Blue = water

• Green = forest

• Brown = contour lines

• Black = cultural features (buildings, place names, boundary lines, roads, etc.)

• Red = principal roads

• Pink = urban areas

• Purple = revisions to an older map, compiled from aerial photos. If an area has become urbanized, this may be shown as purple shading on the new, revised map.

1.7.5 Symbols

A variety of topographic map references give the key for common map symbols, including boundaries, roads, buildings, railroads, types of vegetation, marshes, quarries and mines, water and coastal features, etc. check meaning of topographic map symbols is online at http://erg.usgs.gov/isb/pubs/booklets/symbols/.

1.7.6 Latitude and Longitude

Latitude and longitude are the basic tools of mapmaking. They are the language used by mapmakers to communicate accurately about the locations of the various places on planet earth.

Latitude and longitude are imaginary lines traced on the surface of the earth for the purpose of locating a specific place. The lines of latitude run east and west, and are parallel to each other. For convenience, the earth has been divided into 360 degrees of latitude. Measure of latitude starts at the equator and is measured as 90 degrees north to the North Pole and 90 degrees south to the South Pole. Each degree represents 60 nautical miles on the earth's surface. The lines of longitude run north and south and are not parallel to each other. Consecutive degrees of longitude are 60 miles apart at the equator, and all come together at the North Pole and the South Pole. These are 360 degrees of longitude - 180 degrees lie east, and 180 degrees lie west of Greenwich, England, an arbitrary starting point used by all mapmakers.

All lines of longitude are called "Great Circles" because they are all representative of the circumference of the earth. Only one latitude line is a great circle, the one lying on the equator. All other latitude lines are smaller than the circumference of the earth.

Since earliest times, astronomers and mapmakers have used the equator to divide the world into northern and southern hemispheres. The starting point for longitude, however, has varied many times over the ages. It has been located in Egypt, Greece, Spain, France, and other places, depending on which country was preeminent at the time in the study of location by celestial observation. In 1884, the international community adopted Greenwich as the mean in order to standardize world mapmaking.

The use of grid lines (latitude and longitude) was first suggested by the Greek astronomer Hipparcus about 300 years before Christ. Shortly after, Hipparcus devised the method of fixing the location of places on earth by observation of the celestial bodies--the sun, moon and stars. He worked out the mathematics of spherical trigonometry, which allowed the results of these observations to be plotted on an earth that he perceived to be a sphere.

Some 75 years later (around 225 B.C.) Eratosthenes, another Greek mathematician and astronomer, measured the circumference of the earth (accurate to within 300 miles) raising the art of mapmaking to new standards of accuracy.

From that point on, the Greeks could find latitude quite easily. They knew the position of the sun north or south of the equator. By using spherical trigonometry they could measure the sun's angle at noon relative to the equator. Noon was easy to determine since it occurred when the sun was at its highest point in the heavens.

Longitude, however, was not so easy. The distance from one place to another on the earth in an east-west direction could be plotted from the position of the stars and sun, but only if the time difference between the two places was known. The measurement of longitude was to remain inexact until the invention of the telescope and the accurate clock, almost two thousand years later.

A way of longitude by measuring the time lapse in observing the eclipses of the satellites of Jupiter, became possible with the invention of the telescope. While this was difficult, it did provide some progress toward the measurement of longitude. This solution, however, was restricted to use on land since the eclipses could not be accurately observed on the deck of a moving ship.

Accurate clocks, which began to appear in the 16th century, made longitude measurements on land a reality. It was not until 1760, however, that an Englishman named John Harrison invented an exact chronometer, making possible the measurement of longitude at sea.

Today, with the aid of satellites, someone with the proper instruments on even a small yacht can measure latitude and longitude at sea to within an accuracy of 50 feet.

The edges of many topographic maps are bounded by lines of latitude and longitude. The size of the sheet is given in degrees, minutes, and seconds.

For latitude and longitude:

1 degree (1°) = 60 minutes (60')

1 minute (1') = 60 seconds (60")

The lines that run east and west, bounding the top and bottom of the map are latitude lines. Look at the left and right top corners of the map to see the latitude of the line that forms the top (northern) edge of the map.

The lines that run north and south, bounding the left and right sides of the map are longitude lines. Look at the top and bottom corners on the left to see the longitude of the line that forms the left (western) edge of the map.

Intermediate latitude and longitude lines (for various seconds or minutes) are found along the edges of the map. Please note that the degrees may have been left off (as an abbreviation), and you may see only minute and second designations. The degrees are listed only at the corners on most maps.

Also note that there are other numbered lines on the map and tick marks along the map edges. Some of these are other systems of measurement, such as Universal Transverse Mercator (UTM) lines. If you are looking for latitude and longitude markings, you will need to ignore these other lines and tick marks. Look for the tick marks labeled with minutes (') and seconds (").

Maps covering 7.5 minutes (7.5' or 7'30") of latitude and longitude, and maps covering 15 minutes (15') of latitude and longitude are common. Maps covering a large region are typically 1° x 2° quadrangles, or 30' x 60' quadrangles.

Topographic maps at the equator that cover 7.5' x 7.5' are basically square. The 7.5' x 7.5' maps become narrower as you approach the poles because the lines of longitude converge pole ward.

1.7.7 Coordinates

Maps may contain coordinates, marked along the borders, that are usually shown as measurements of latitude and longitude: These help the map user know where the area is in terms of the equator and other points east or west of another main point, such as London or Washington.

1.7.8 Scale

Maps usually also have a scale that shows common measurements, such as miles or kilometers in reference to the map. Sometimes they also indicate this as a ratio, as when they say that the map is drawn at 1:20,000 scale, meaning that one unit on the map (say, an inch) equals 20,000 of those same units (again, inches) in real life

Scale is the relation between the size of the map and the size of the real area, on the ground. There are three ways to represent the scale of a map:

· Verbal scale - such as saying "1 inch = 5 miles".

· Bar scale (or graphical scale) - indicated by a line or bar with distances marked in miles, feet, or kilometers.

· Ratio scale (or fractional scale) - a fraction representing the relationship between one unit on the map and one unit on the ground. Example: 1:24,000 or 1/24,000. This ratio (or representative fraction) indicates that "one unit on the map is equal to 24,000 units of the same size on the ground." This holds true for any units. You may consider the units to be inches, centimeters, feet, or any other unit of measure. The units are always the same on both sides of the fraction. It is the proportion between the map and the real world that is being expressed. Simple mathematics can convert a ratio (or fractional scale) to any desired comparison of units.

1.7.9 Compass Rose

Maps usually have a compass rose or some other symbol, such as an arrow, that helps orient the map user to direction: Usually, but not always, north is at the top of the map.

1.7.10 Legend

Maps usually have a legend that explains the symbols used for example, rivers as blue lines or railroads as lines with cross markings.

1.7.11 Cartouche

Many maps have a cartouche, a sometimes elaborate feature that contains the title of the map, name of the cartographer and/or sponsor, and publication information such as the date and place of publication. The cartouche may also contain other graphic designs, such as landscape images or illustrations of people, animals, plants, etc.

1.7.12 Sheet name

Sheet name and location is generally found in the upper and lower right corners of the map. The sheet is named for a town or other feature in the sheet. The names of the surrounding sheets are present in small letters along the edges at the corners of the map.

Identify the marginal information found on the legend.

a. Marginal information at the top of the map sheet.

· The top left corner contains the geographic location of the map area and the scale of the map.

· The top center has the name of the map sheet.

· The top right corner contains the map edition, map series, and the map sheet number.

b. Marginal information at the bottom of the map sheet.

· The lower left corner of the map contains the legend, the name of the agency that prepared the map, the map sheet number, and the map sheet name.

· The bottom center contains the bar scales in meters, yards, miles, and nautical miles; the contour interval of the contour lines; the grid reference box; the declination diagram; and the G-M angle (mils or degrees).

· The lower right corner contains the elevation guide, the adjoining map sheet diagram, and the boundaries box, which shows any boundaries that may be on the map.

1.7.13 Commentaries

Maps may also include written commentaries that describe aspects of the history, geography, or politics.

1.7.14 Neatline

As they finish their maps, cartographers often frame them with a border called a neatline. All of the parts mentioned above tend to vary through time as cartographers use different styles.

1.8 Cartographic Methods of Presentation

Graphic methods used on maps to show the spatial arrangement of phenomena and their combinations, relationships, and development. A special system of characters—the cartographic symbols, which are summarized and systematized in a relatively small number of cartographic methods of presentation—is used in cartography for this purpose. The primary methods include those of signs, line symbols, isolines, and the qualitative background; angle diagrams; the point method; area patterns; signs of motion; and collation and choropleth maps.

The sign method (nonscale signs) is used for objects that are not expressed in the scale of the map and are usually used to represent phenomena that are localized at points. The signs indicate the location and type of the objects and may also describe their size, importance, or change over time (for example, symbols for populated points that indicate the type of settlement, population, and administrative significance). The shape, size, and color of the signs are used to represent the characteristics of the objects being mapped. The symbol may have a geometric shape, it may be a letter of the alphabet, or it may resemble in outline the object being represented. Geometrically shaped signs whose area is proportional to the numerical index of the objects being shown are often used—for example, proportional to the number of workers when mapping industrial enterprises or centers.

Line symbols are used to show political and administrative borders and power lines and for linear objects whose width is not expressed in the scale of the map (for example, roads and rivers). The qualitative and quantitative characteristics of linear objects are shown by the type of lines (for example, various dotted lines) and the color and the width of the symbols.

The isoline method is used to convey the quantitative characteristics of phenomena that are continuous and change gradually in space (for example, terrain and climatic phenomena).

The qualitative background method shows the breakdown of a territory (its regionalization) according to some particular natural, economic, or political and administrative features. It is used for qualitative description of phenomena that are continuous over the earth’s surface (for example, soil cover) or have a large-scale scattered distribution (for example, population). The first step is the development of a classification of the phenomenon being mapped; the territory then is divided according to the classification into qualitatively homogeneous parts (districts, regions, and so on). Finally, areas belonging to the same class are given the color assigned to the particular type or hachured accordingly.

Angle diagrams (that is, diagrams related to definite points) are used to describe seasonal and other periodic phenomena (the annual course of temperatures and precipitation; changes in snow cover), the frequency and velocity of winds from various directions (in the form of wind roses), and the frequency and velocity of ocean currents.

The point method is used to map large-scale scattered phenomena (rural population, croplands, and livestock farming). For this purpose a definite number of objects (units) is symbolized by a point (more precisely, a small circle) located at the place on the map where the objects actually exist. As a result a certain number of points of equal magnitude and identical significance are written on the map; their grouping (density) gives a graphic picture of the location of the phenomenon, and their number makes possible determination of its dimensions or the number of objects.

Area patterns, or areas of distribution of some particular phenomena (various species of plants and animals; various types of farmland) are shown on maps by contouring a section with a solid or dotted line of definite design or by coloring or hachure. The diversity of methods for representing ranges makes possible the combination of a number of ranges on the same map, even if they overlap.

Signs of motion are used for natural and social phenomena (ocean currents, migration of birds or population, shipping, and directions of military strikes).

Graphic methods are widespread, above all vectors (arrows), which may be used to characterize the speed, stability, power, and other features of the phenomena by differences in their shape, size, and color. A second common method is bands (strips) for passenger and cargo flows, which are laid out along the routes of movement; their width usually indicates the size of the flow.

Collation and choropleth maps are used for a graphic spatial representation of statistical data (for example, population data) that are being processed or published in summary form, as applied to administrative or other territorial divisions rather than individual points or objects. Collation maps show the distribution of a phenomenon by means of diagrams that are located within units of the territorial grid and express the total magnitude of the phenomenon (for example, the amount of arable land) within the borders of each territorial unit. The choropleth map is a method of showing the average intensity of a particular phenomenon (average population density, percentage of land under cultivation, and so on) within definite territorial units, most often administrative units. In this case each territorial unit is colored or hachured so that the intensity of the color or hachure indicates the intensity of the phenomenon.